The present invention relates to a method of effecting a smooth changeover between at least two binary datastreams, by minimizing the phase difference between the datastreams prior to changeover, said method comprising the steps of:
Feeding the datastreams into a phase synchronizing device. PA0 Comparing the binary amplitude of respective datastreams. PA0 Determining a value of the phase difference between said datastreams. PA0 Delaying the datastreams in relation to one another until acceptable phase similarity is achieved. PA0 Effecting changeover between the datastreams.
The invention also relates to an arrangement for carrying out the method.
When transmitting data between a transmitter and a receiver unit, redundant transmission is essential if reliability is to be achieved. By redundant data transmission is meant in this particular case the transmission of two similar datastreams to one and the same receiver from one and the same transmitter, although by means of different transmission devices. The object of this type of redundant transmission is to enable the receiver to switch to a more favourable transmission device in the event of a disturbance in or malfunction of one of the transmission devices.
In order to achieve smooth or undisturbed changeover between two binary datastreams without losing data bits, it is necessary for the two datastreams to be essentially in phase with one another at the time of the changeover. Prior publication EP 249,930 discloses a method and an arrangement for synchronizing two binary datastreams prior to changeover. According to the known method, each of the two datastreams is blocked in a respective memory buffer and the datastreams are led from the outputs of said buffers to an amplitude comparison circuit. Depending on the output signal of the amplitude comparison circuit, it is possible to prevent the infeed of data into one of the buffers until satisfactory phase similarity is achieved between the datastreams leaving the buffers, whereafter a changeover between these datastreams can take place. One problem with this known technique is that phase synchronization prior to changeover must be divided into two sequences, namely a sequence in which one datastream is delayed until phase similarity is achieved and a second sequence in which the original data rate is recreated. Furthermore, when practicing the known technique, it is necessary to process data at a speed which corresponds to the speed at which the incoming datastreams are transmitted. This results in an unnecessarily expensive and complex arrangement consisting of expensive, high performance components which are necessitated to operate at a speed which is at least equally as high as the transmission speed of the binary datastreams.